Described below are a transcoding method and a transcoding device.
In many applications video signals are provided at a number of quality levels. Examples of this are:                Digital TV at a number of quality levels for receivers (home TV devices, PCs, organizers, multimedia-enabled mobile terminals),        Individual video services for different terminals and access points (broadband cable, XDSL, ISDN, UMTS)        Pay TV and other video services, with video signals of better or worse quality being provided depending on the selected charge category.        
Concepts have been presented for such systems in which the individual video signals are not encoded independently of each other (simulcast), but video signals of higher quality levels are derived from video signals of lower quality levels (differential encoding). See K. Illgner, J. Pandel, “Effiziente Codierung von Videosignalen für skalierbare Multicast-Speicherung und —Übertragung sowie zugehöriger Codec” (efficient encoding of video signals for scalable multicast storage and transmission as well as associated codec), publication DE 102 00 901 A1, and P. Amon, G. Bäse, J. Pandel, “Prädiktion von Videosignalpegeln für skalierbare Simulcast-Speicherung und —Übertragung” (prediction of video signal levels for scalable simulcast storage and transmission), file reference of German patent application DE 101 46 220.4. One of the ways in which efficient differential encoding is made possible is the synchronization of the encoding units during the encoding for the different quality levels. Such a method is known from P. Amon, K. Illgner, J. Pandel, “Verfahren zum Codieren und Decodieren von Videosequenzen und Computerprogrammprodukt” (method for encoding and decoding of video sequences and computer program product), Publication DE 102 19 640 A1. Synchronization in this context means that decisions are made only once relating to the encoding of an image or of part of an image in the various encoding units of the individual quality levels.
On the receiver side a plurality of encoded image data of the different quality levels is combined in the decoder and the video signal associated with the respective quality levels is reconstructed. A possible implementation of this type of decoder is known from citations in the Background section.
For a few applications it is however desirable for only a video signal at a specific level of quality to be provided. For example it is only possible for a mobile radio terminal to decode just one video signal for reasons of complexity. In a further scenario only the video signal with the lowest quality level is to be decoded and displayed in a PC. In this case it can be necessary in practice only to transit that video signal which corresponds to the lowest quality level.